Transfer of organic matter between wastewater and activated sludge flocs

The organic matter of wastewater was fractionated into settleable (i.e., pa rticulate) and non-settleable (i.e., colloidal+soluble) fractions by settli ng followed by 0.22 mum filtration. Particulate, colloidal and soluble prop ortions were found to be relatively constant (45, 31 and 24% of the total C OD, respectively). Transfer of soluble fraction always occurred from the wa stewater to the activated sludge flocs, whereas bidirectional transfer occu rred for the colloidal fraction. The transfer of soluble and colloidal matt er reached a steady state after 40 min-mixing and 20 min-mixing, respective ly. Desorption of a part of the colloidal organic matter pre-sorbed on the activated sludge flocs was evidenced. The biosorption capacity of activated sludge was around 40-100 mg(COD)gT(SS)(-1). The biosorbable fraction of wa stewater represented on average 45% of the non-settleable fraction. (C) 200 0 Elsevier Science Ltd. All rights reserved.